Broadband data and video services, on which our society and economy have grown to depend, have heretofore generally not been readily available to users on board mobile platforms such as aircraft, ships, trains, automobiles, etc. While the technology exists to deliver such services to all forms of mobile platforms, past solutions have been generally quite expensive, low data rate and/or available to only very limited markets of government/military users and some high-end maritime markets (i.e., cruise ships).
At present, a wide variety of broadcast television (TV) services are available to terrestrial users via satellite links. Such services include commercial Direct Broadcast Satellite (DBS) services (such as DirecTV□ and EchoStar□) and custom video, such as rebroadcast video, over private Fixed Satellite Services (FSS) or Broadcast Satellite Services (BSS) satellites. The data services which can be provided via satellite link include all conventional Internet services (e.g., email, web browsing, NetMeeting, etc.), as well as virtual private networks (VPNs) for corporate and government customers.
Previously developed systems which have attempted to provide live TV and data services to mobile platforms have done so with only limited success. One major obstacle has been the high cost of access to such broadband data and video services. Another problem is the limited capacity of previously developed systems, which is insufficient for mobile platforms carrying dozens, or even hundreds, of individuals who each may be simultaneously requesting different channels of programming or different data services. Furthermore, presently existing systems are generally not readily scalable to address the demands of the traveling public.
Certain services currently available provide a limited subset of the above described services. One such service provides a narrow-bandwidth Internet connection to users on a mobile platform. Another service provides either TV broadcast services from available direct broadcast signals (i.e., EchoStar and DirectTV) or provides a custom TV broadcast signal through dedicated satellite links (i.e., Airshow). However, no system or method presently exists for providing high speed (i.e., greater than 64 Kbps) data networking services to groups of users on mobile or remote platforms, let alone for providing such high-speed networking services together with video services.
There are several operational systems that provide limited Internet data services on commercial airlines and cruise ships. These systems are very limited in their link capability (primarily use communication links developed for telephony) and the service is very expensive (greater than about $1.00 per minute for voice connection). For these reasons, and in view of adherent limitations on the capacity of such systems, such systems have met with limited commercial success and acceptance.
Current operational systems generally use Inmarsat satellite communication links or terrestrial wireless communication links (i.e., the National Air Telephone System “NATS”) to achieve 2-way connectivity to mobile platforms. These connection forms have several drawbacks:
1) a limited connection bandwidth (typically less than 64 Kbps);
2) limited overall system capacity (due to limited frequency spectrum); and
3) high expense.
Inmarsat operates in the L-band frequency spectrum, where there is very little bandwidth and capacity available for providing broadband services to the traveling public. NATS based solutions (i.e., GTE Airfone□, AT&T Claircom), familiar to domestic airline travelers who use seat back-mounted telephones, also provide very limited capacity because of operation at L-band. These systems also suffer from the additional problem that connectivity is only available over land.
Current mobile platform connection methods are inherently narrow band and restrict the flow of data to the point where common networking tasks are impossible. Typically, this connectivity is achieved through the use of a standard computer telephone modem between the user's computer and the air-ground or ship-shore telephony system. In this scenario, each user gets exclusive use of a full communications channel for the duration of his/her networking session and effectively prevents others from using that portion of the telephony system.
With present day systems which attempt to provide a means by which a plurality of mobile platforms transmit data to a shared satellite-based transponder, a particularly troubling problem has been how to efficiently operate and manage a plurality of small aperture mobile transmitting terminals that are geographically distributed over a wide area, with each mobile terminal transmitting at a different power spectral density (PSD) level according to its specific aperture size, the location of the mobile platform and the data rate at which data is being transmitted. It will be appreciated that airborne antennas such as electronically scanned phased array antennas (PAAs) tend to be smaller in aperture size than conventional terrestrial antenna. This is because of the important requirement for low aerodynamic drag of the antenna. Therefore, mobile platform based transmit antennas tend to have wider antenna beams than conventional terrestrial Very Small Aperture (VSAT) antennas (typically about one meter diameter aperture). As a result, they radiate more power to adjacent satellites along the geostationary orbit (GSO) plane. Also, mobile transmit antennas can interfere with communications on satellites in non-geostationary orbits (NGSOs). Put differently, such mobile transmit antennas can easily produce signals that interfere with the operation of GSO and NGSO satellites that are adjacent to the target satellite.
There are strict regulatory requirements imposed by regulatory agencies such as the Federal Communications Commission (FCC) and International Telecommunications Union (ITU) on the maximum power spectral density (PSD) that can be radiated to adjacent GSO and NGSO satellites. When a plurality of mobile platforms are transmitting RF signals to a common transponder within a given coverage region, it becomes very difficult to manage the PSD of individual mobile platforms to ensure that the “aggregate” PSD never exceeds the regulatory limits, while simultaneously attempting to maximize the total number of mobile platforms accessing the transponder.
One previously developed approach for dealing with the above-described problem of managing the transmissions of a plurality of transmitters accessing a single transponder has been to employ multi-channel-per-carrier (MCPC) operation. With this method, which was developed by Intelsat, each VSAT antenna is allocated a portion of the satellite transponder bandwidth. In other words, this method uses frequency division multiple access (FDMA) to allow multiple terminals to simultaneously access the transponder. Using this technique, only one terminal (carrier) is transmitting in each channel at a PSD below the regulatory limit. This method of operation is wasteful of PSD because the unused PSD in each channel cannot be used. Furthermore, MCPC cannot be adapted to efficient PSD operation because channel management becomes prohibitively complex, especially for applications using mobile terminals. This invention provides a simple link management solution for mobile platforms having time varying PSDs. Similarly, time division multiple access (TDMA) methods have only one terminal accessing a channel or time slot at any time so that the available channel PSD is fixed and usually exceeds the requirements of the channel user. Therefore, PSD is wasted and cannot be reused. With these previously developed methods, individual accesses do not usually occur at the maximum allowable PSD, so that there will usually be some amount of PSD that is unused or wasted in every channel. This is the primary drawback of all previously developed methods.
The above described scenarios where only one terminal is transmitting within a channel or time slot at any given time thus present the classic problem of allocating a fixed size resource (i.e., PSD) to variable sized users. The fixed size resource must then be sized for the worst case (i.e., maximum PSD) user so there will always be inefficiency with these approaches. If the variations between users is small, then the inefficiency can be reasonably low, but for any other application where there are large differences in user PSD requirements, the inefficiency becomes substantial.
Still another prior developed method of dealing with multiple terminals accessing a single transponder is code division multiple access (CDMA), whereby a single channel is shared by multiple users. More efficient operation can be achieved with CDMA because large pools of users share a common resource (i.e., the transponder). Most CDMA systems operate without restriction on aggregate PSD (such as cell phone systems, for example). Typically, user terminals or handsets transmit with a power level required to overcome interference, without any regulatory restrictions on aggregate PSD. With this method of operation there are statistical variations in PSD levels and interference between users that would be unacceptable for high-quality satellite data communication systems. In contrast, satellite based communication systems often must operate within strict regulatory limits on aggregate PSD. This is especially critical in the Fixed Satellite Services (FSS) portion of the Ku-band, where Mobile Satellite Services (MSS) have been given a secondary frequency allocation by the ITU, and must guarantee non-interference with primary FSS systems. Thus, managing CDMA satellite systems in a PSD limited environment requires new methods for managing the aggregate PSD produced by all of the user terminals, especially when the terminals are to be disposed on mobile platforms such as aircraft.
It is therefore a principal object of the present invention to provide a system and method for managing the aggregate PSD produced by a plurality of mobile terminals operating within a given coverage region, and accessing a shared satellite-based transponder, such that the aggregate PSD does not exceed regulatory PSD limits for interference with GSO and NGSO satellites.
It is still another object of the present invention to provide a system and method for using a central control system to monitor the PSD of each one of a plurality of mobile terminals operating within a given coverage region and accessing a shared satellite-based transponder, and to ensure that the aggregate PSD of the RF signals to be transmitted by the mobile terminals does not exceed a predetermined regulatory PSD limit and which is used to authorize RF transmissions by each of the mobile terminals.
It is still a further object of the present invention to provide an apparatus and method for monitoring and authorizing transmissions from a plurality of mobile terminals which each produce RF signals having differing PSDs, and which operates to manage access to a satellite-based transponder by the mobile terminals such that the aggregate PSD of the transmissions from all of the mobile terminals does not exceed a predetermined regulatory PSD limit. It is a further object of this method to provide a control system that will deny access to the satellite-based transponder if such access would cause the aggregate PSD to exceed the predetermined regulatory PSD limit, and to permit access to the transponder if the aggregate PSD is below the regulatory limit.